1. Field of the Invention
The present invention relates to a mobile communication system for providing communication services to user equipments, the user equipment in the mobile communication system, a control program thereof, and a synchronization establishment determination method in the mobile communication system.
2. Description of the Related Art
In recent years, a mobile communication system using W-CDMA (Wideband-Code Division Multiple Access) has been used as a multiple access method.
In the mobile communication system using the W-CDMA (hereinafter appropriately referred to as “W-CDMA wireless system”), in a user equipment (UE), synchronization establishment determination is performed based on a reception quality of a signal received from a base station, and if the received signal has the reception quality higher than a certain reception quality, it is determined that synchronization has been established.
As such a synchronization determination method, for example, a method of performing the synchronization establishment determination based on a BER (Bit Error Rate) in a pilot signal of a DPCCH (Dedicated Physical Control CHannel) has been known (see JP2006-67002A).
However, transmit power control in the W-CDMA is performed based on the BER of TPC (Transmit Power Control) bits, and according to a specification of the W-CDMA, it is accepted that a transmitted wave power of these TPC bits and a transmitted wave power of the pilot signal may be different from each other.
In other words, the synchronization establishment determination based on the BER of the DPCCH pilot signal is not necessarily accurate, and the determination can be performed more accurately in the synchronization establishment determination based on the BER of the TPC bits which represent a communication state more directly.
Incidentally, if the synchronization establishment determination is performed based on the BER of the TPC bits, a pattern of the TPC bits transmitted from a communication network side to the user equipment cannot be known on the user equipment side, and thus it is difficult to directly measure the BER of the TPC bits.
Consequently, it is conceivable to estimate the BER of the TPC bits by using the DPCCH pilot signal of which known pattern has been transmitted from the communication network side.
However, in the W-CDMA, diversity transmission may be performed in the base station. For example, if the diversity transmission with two systems of 0-system and 1-system is performed, when a phase difference in transmitted waves of the respective systems becomes approximately 180 degrees (out of phase), it is estimated that the transmitted wave power of the TPC bits becomes approximately zero, since the TPC bits have no orthogonality in transmitted signals of the 0-system and the 1-system (that is, the transmitted signals are the same in both the 0-system and the 1-system). This leads to a situation where it is determined that the synchronization cannot be established in spite of a communication state in which the synchronization can be actually established.